S2 Unit 3 -

Fossil

preserved remains or traces of a once-living organism that lived in the past

Fossil record

history of life documented through fossils

Importance of fossils found in Australia for evidence of megafauna existence

The fossils may be parts of the megafauna, so finding these fossils in australia and dating them will help give evidence for their existence and when they existed.

isotope

Atoms with the same number of protons, same place on the periodic table (the same chemical element), but different number of neutrons

relative atomic mass

average weighted mass of all isotopes of an element

difference between the structure of an isotope and atom

Isotopes have a different mass number due to the different amount of neutrons it has

how the relative mass of an element is calculated

(Mass number of isotope x abundance (%)) + (Mass number of isotope x abundance (%)) = Total Mass number of isotopes/100

radioactive decay

Unstable isotopes that decay/change into another isotope and produce alpha, beta, and/or gamma radiation

radioisotope/radionuclide

An unstable isotope that breaks down

 alpha radiation

The nucleus ejects an alpha particle (a). This only occurs to atoms with very heavy nuclei, such as a mass number of over 100.

alpha particle

2 protons, 2 neutrons (aka helium)

charge and speed of alpha radiation (charge, speed)

+2, 10% speed of light

beta radiation

a beta particle leaves the atom, and a neutron in the nucleus decays into a proton

beta particle

electron

charge and speed of beta radiation (charge, speed)

-1, 90% speed of light

gamma radiation

Emission of gamma rays after alpha or beta particle leaves atom when nucleus is still excited

gamma rays

high energy electromagnetic rays. comparable to high energy x-rays

charge and speed of gamma radiation (charge, speed)

0, speed of light

relationship between a half-life and the number of atoms of a substance

when you find the half-life of a radioisotope, half of the atoms in the substance have decayed

examples of radioisotopes

Carbon-14, hydrogen-3, lithium-5

 risks associated with radioactivity

When a person comes in skin contact with a radioactive object, the DNA can be damaged in the person’s cells and cause health issues

carbon dating

The dating of organic samples that must contain carbon. It works by measuring the ration of carbon-14 to carbon-12. The less carbon-14, the older the sample.

how the half-life of a radioisotope can be used to ‘tell time

When the half-life is determined, the absolute age of a sample can be found.

how the known half-life of radioisotopes can be used to determine the age of megafauna

By multiplying the half-life by two, you can find out when the decay (death) of the megafauna occurred, therefore find out how long ago they existed

how carbon dating has been used to establish that Aboriginal Peoples have been present on the Australian continent for more than 60,000 years

absolute dating

determines the actual age of a sample in years

relative dating

determines whether a sample is younger or older than another

absolute dating techniques

Carbon dating, potassium-argon dating, uranium-thorium dating, dendrochronology

relative dating techniques

law of superstition, correlation of rock strata, fluorine dating

limitations for carbon-14 dating

Only used on organic samples, must be younger than 60,000 years old

limitations for potassium-40 dating

Only used on samples that contain igneous rock, must be older than 200,000 years old

limitations for uranium-238 dating

Only used on samples that contain sea sediment or coral, must be younger than 600,000 years old

strong nuclear force

Holds protons and neutrons in the nucleus together. The electric force between protons makes them repel each other, however the nuclear force counteracts the electric force, because it is more attractive and stronger in extremely small distances.